European Patent Application No. 313 563 describes a method and a device for wheel position measurement, using a rotating gyroscopic device suspended by a universal joint. An angle measurement device is adjusted to the first wheel. The subsequently started rotation of the gyroscopic device guarantees that the rotation axis of the gyroscopic device, which is used as a reference axis, does not change during the subsequent measurement procedure. The angle measurement device is mounted on the next wheel, and the angle formed between the wheel and the reference axis is measured. This procedure is repeated for all wheels. The differences in orientation of the other wheels compared to the first wheel are measured, stored, and subsequently compared to one another in order to determine the wheel adjustment values. The start-up time of the gyroscopic device used as the reference axis is approximately 15 minutes if a high degree of accuracy is required. As an additional angle transducer required in addition to the gyroscopic device, an incremental angle transducer measures the angle difference between the initial position and the measured position.
The device for axle alignment of a vehicle according to the present invention, which allows at least one angle to be determined between a wheel of the vehicle and a reference direction, provides that the angle is determined using a transducer having at least one rotation speed sensor, whose output signal is integrated. The use of rotation speed sensors for axle alignment makes it possible to dispense with an exact alignment of the transducers with respect to one another on each wheel of the vehicle. Long setup and adjustment times are avoided. Since each transducer used for axle alignment assumes a known relative position with respect to the reference direction, which does not depend on the vehicle or the arrangement of another transducer, large axle bases or axle offsets of the vehicle to be aligned have no importance. The transducer can be equally used for passenger cars, trucks, trailers or multiaxle vehicles. The rotation angles obtained by integration are used as a measure for a trail angle or camber angle of the vehicle. The rotation angle provides the deviation of the rotation axis coordinates of the wheel from the reference direction. This angle is used as basic data for the algorithm used to determine the trail angle or camber angle.
In one exemplary embodiment, one transducer has three rotation speed sensors forming an orthogonal system. Thus the reference direction can be completely isolated from the vehicle. All information required to compensate interference caused by translational motion is obtained.
In an exemplary embodiment of the axle alignment method according to the present invention, a transducer is provided, which has at least one rotation speed sensor whose output signal is integrated. The transducer is adjusted so that it assumes a known position with respect to a reference direction. Subsequently it is mounted on one wheel of the vehicle. The angle formed is a measure of a trail or camber angle of the vehicle wheel. The rotation speed sensor measures the relative position of the transducer with respect to the reference direction. The transducer no longer has to be arranged in a predefined position on the vehicle wheel. Time-consuming adjustment procedures thus become unnecessary.
In a particular embodiment, a third step is provided, in which the relative position of the rotation axis coordinates of the wheels with respect to the reference direction is determined. Angular offsets of the wheel axles that occur with respect to one another provide information on the correction measures on the axle geometry to be taken.
The particular embodiment of the present invention provides for the compensation for the earth""s rotation during angle measurement, increasing the accuracy of angle measurement. Since the rotation speed sensor measures these interfering quantities continuously at rest, a low-maintenance, self-calibrating system can be created.
In a fourth step of a useful refinement, the transducer is set to the same position as in the first step. The previous measurement is then invalid if the angle obtained in the fourth step differs significantly from zero. Interference affecting the measurement can be controlled without major expense. This measure contributes to more userfriendly automation.